The effect of maternal cigarette smoking during pregnancy on fetal growth and survival are profound. Relationships to subsequent child development are problematical. Some past studies have found strong association, others only weak ones. These studies have been plagued by unrepresentive populations, small numbers or weak design and analysis, or cgmbinations of these flaws. We are studying this issue in a large, representative population (all 17,000 children born in Britain during one week in 1970) already assessed at birth and age 5 and now being tested at age 10. By use of longitudinal assessment, we can test for differences is social drift between smokers, ex-smokers over time, and with extensive cross sectional social data, can test whether stratification by social class based on husbands occupation only partially controlled for real social difference. In addition, we are studying whether maternal smoking is associated with differences in the quantity and quality of preschool education provision. If differences in child developmental indices are associated with maternal smoking, we will test whether they are indirectly, and therefore more likely to be non causally, related. The outcome measures include somatic growth, and measures of both mental ability and achievement. The entire cohort was assessed at birth and age 5.